U.S. patent application Ser. No. 12/431,035, filed Apr. 28, 2009, is hereby incorporated herein by reference and discloses methods for monitoring the operability of a GPS receiver in order to determine, or verify, the validity of global positioning satellite signals being received by the receiver.
U.S. Pat. No. 7,305,928, issued Dec. 11, 2007, is hereby incorporated herein by reference and discloses vessel positioning systems that maneuver a marine vessel in such a way that the vessel maintains its global position and heading in accordance with a desired position and heading selected by the operator of the marine vessel.
U.S. Pat. No. 7,267,068, issued Sep. 11, 2007, is hereby incorporated herein by reference and discloses systems wherein a marine vessel is maneuvered by independently rotating first and second marine propulsion devices about their respective steering axes in response to commands received from a manually operable control device, such as a joystick. The marine propulsion devices are aligned with their thrust vectors intersecting a point on a centerline of the marine vessel and, when no rotational movement is commanded, at the center of gravity of the marine vessel.
U.S. Pat. No. 6,485,341, issued Nov. 26, 2002, is hereby incorporated herein by reference and discloses methods for controlling the average speed of a vehicle over a time period or distance length and includes selecting a desired average speed, measuring an actual speed, and maintaining a cumulative error determined as a function of the difference between the average speed and actual speed at the time over which the actual speed measurement was taken.
U.S. Pat. No. 6,273,771, issued Aug. 14, 2001, is hereby incorporated herein by reference and discloses control systems for a marine vessel that incorporate a marine propulsion system that can be attached to a marine vessel and connected in signal communication with a serial communication bus and controller.
GPS receivers are commonly utilized to calculate and provide a current global position of a marine vessel. The global position is communicated to a control system, which automatically controls operation of a propulsion system of the vessel based upon the global position. This allows the control system to, for example, maintain a desired global position of the vessel or maintain a heading and/or speed of travel of the vessel.
Those having ordinary skill in the art of GPS receivers and control systems for the marine vessels understand that from a plurality of GPS signals received from GPS satellites, a microprocessor in the GPS receiver is able to calculate and provide to the control system: the longitude and latitude where the GPS receiver is located, the speed over ground (SOG) and the course over ground (COG) of the GPS receiver (and by association the SOG and COG of the marine vessel in which the GPS receiver is located), and the number of and location of the GPS satellites in terms of, for example, relative distance and azimuth from the GPS receiver. In some cases the GPS receiver is also able to calculate and provide to the control system the horizontal dilution of precision (HDOP) of the plurality of GPS signals. HDOP is a standard GPS accuracy metric that is largely based upon the geometric position of the satellites being used by the GPS receiver.